1. Field of the Invention
The present invention generally relates to optical disks, and more particularly to an unauthorized use prevention method, and an optical disk having an unauthorized use prevention function. Further, the present invention is concerned with an optical disk apparatus for reading data from an optical disk having such an unauthorized use prevention function.
2. Description of the Prior Art
An optical disk has a large data storage capacity, and data can be easily read from the optical disk and recorded thereon by a random access method. From the above point of view, optical disks have been widely used. In the specification, the term "an optical disk" includes a magneto-optical disk.
With the spread of use of optical disks, the problem of data recorded on an optical disk being unlawfully copied onto another recording medium becomes significant. Hence, it is necessary to provide an unauthorized use prevention method in order to facilitate the spread of use of optical disks while the copyright of data and programs recorded on the optical disks is protected.
FIG. 1 is a block diagram illustrating an overview of a conventional optical disk apparatus. The optical disk apparatus shown in FIG. 1 is made up of a host computer 10, an optical disk drive 11, and a SCSI (Small Computer Systems Interface) unit 12. An optical disk 1 is loaded in the optical disk drive 11 via a disk inserting opening 11a. The optical disk drive 11 reads data from the optical disk. In some apparatus, the optical disk drive 11 has the function of recording data on the optical disk 11. The host computer 10 and the optical disk drive 11 can communicate with each other via the SCSI unit 12.
FIG. 2 illustrates the format of the optical disk according to the ISO (International Standards Organization) standard (ISO 10090), the disclosure of which is hereby incorporated by reference. A user accessible area A is composed of tracks between the third track and the 9996th track. The user accessible area A can be used in one of the following manners. The whole user accessible area A is used as a RAM area (also referred to as a rewritable area), or a ROM area. Alternatively, as shown in FIG. 2, the user accessible area A includes a ROM area 15 and a RAM area (rewritable area) 16 (a partial ROM type). Data can be magnetically recorded on the RAM area. Data can be recorded on the ROM area by forming pits on the recording surface.
Three tracks located further out than the user accessible area A function as a DMA (Defect Management Area) B, which is not allowed to be accessed in a normal mode by the user. Data necessary for disk management is recorded on the management area B. For example, data indicating the address range of the ROM area 15 and the address range of the RAM area 16 is recorded on the defect management area B. Data recorded on the defect management area can be accessed in a maintenance mode. Similarly, three tracks are located further in than the user accessible area A. Outer control tracks are formed in an area C located further out than the outer defect management area B, and inner control tracks are formed in an area C located further in than the inner defect management area B. A blank area D is provided further out than the outer control track area C, and a blank area D is provided further in than the inner control track area C.
Normally, the areas B, C and D are referred to as the user inaccessible areas.
Data recorded on the ROM area 15 can be utilized by an application program executed by the host computer 30.
Nowadays, optical disks, on which a variety of data to be protected by copyright is recorded, are sold. For example, data of dictionaries, 10 encyclopedias, novels, game programs and so on are recorded on the optical disks. Hence, it is necessary to prevent data recorded on the optical disks from being unlawfully copied. Particularly, rewritable 3.5 inch optical disks will be widely used.
Japanese Laid-Open Patent Publication No. 60-145501 proposes an unauthorized use prevention method. According to the proposed method, a mark is recorded on an area inherent in a recording medium by physical means. The mark is read from the recording medium and is compared with a reference pattern stored in a reproducing apparatus. When the mark which is the same as the reference pattern is not detected, it is determined that the recording medium is an unlawfully produced recording medium.
Japanese Laid-Open Patent Publication No. 63-26855 proposes another unauthorized use prevention method, in which valid data is recorded on a read only area on a recording medium. Normally, the valid data recorded on the recording medium cannot be read and transferred to a read only area of another recording medium. The valid data is absent in the read only area of the unlawfully produced recording medium.
However, the unauthorized use prevention method disclosed in Japanese Laid-Open Patent Publication No. 60-145501 has a disadvantage in that it needs the physical means for recording the inherent mark on the recording medium and that the inherent mark may be inconsistent with the ISO standard.
The unauthorized use prevention method disclosed in Japanese Laid-Open Patent Publication No. 63-26855 has a disadvantage in that it cannot completely prevent unauthorized copy because the valid data recorded on the read only area can be transferred to an area other than the read only area of another recording medium.